A conventional fuel delivery system for an internal combustion engine typically includes a fuel pump which runs at a constant speed and supplies a constant quantity of fuel to the engine. Since the engine's fuel requirements vary widely with operating and environmental conditions, much of the fuel supplied is not actually needed by the engine and must accordingly be returned to the fuel tank. This returned fuel is generally at a higher temperature and pressure than the fuel in the tank. Returning it to the tank can generate fuel vapors, which must be processed to eliminate environmental concerns.
Returnless fuel systems have been developed to address these concerns. These systems generally determine how much fuel the engine requires at each particular point in time and supply only this required amount of fuel to the engine, eliminating the need to return fuel. A number of engine signals, such as manifold pressure, fuel temperature, and other operating characteristics may be monitored to help determine the required quantity. This requirement is then translated into a fuel pump control signal to control the quantity of fuel pumped to the engine over a specific time period. Such systems often use equations or maintain tables of values which translate the engine signals into actual fuel pump drive data. For example, U.S. Pat. Nos. 5,237,975 and 5,379,741 disclose systems which use lookup tables to translate engine signals into a pump duty cycle.
Feedback is provided in a returnless fuel system to help adjust the fuel supply to meet the fuel demands of the engine. Over time, vehicle wear may change the engine's fuel demand characteristics. Under a given set of operating conditions, a greater or lesser quantity of fuel may thus be required than what was once required under identical conditions when the vehicle was new. Also, fuel system wear and conditions such as a clogged fuel filter, for example, may change the quantity of fuel supplied for a specific pump setting. While feedback eventually accommodates these changes during real time operation, it would be desirable to have an improved system which learns of the changes, incorporates the changes into the base determination of demand, and adapts the underlying tables or equations accordingly. The present invention is directed at making this adaptation.